The broad, long-term objectives of this proposal are to understand how growth factors control the proliferation of animal cells. We wish to define at a molecular and biochemical level the mechanisms by which growth factor signals are transmitted to the nucleus to regulate the transcription of genes involved in the control of cell proliferation. And we would like to understand the basis for the specificity of action of growth factors-how different growth factors elicit distinct biological responses from cells. Our principal experimental focus is the proto-oncogene c-fos, which is rapidly and transiently induced at the transcriptional level as a primary response to activation of several growth factor signal transduction pathways. In this proposal we address a specific model for how such signals activate transcription of the c-fos gene. Our previous work has demonstrated that two different signal transduction pathways act through different protein complexes bound to a common cis-acting regulatory element, the serum response element (SRE), in the c-fos gene. We propose that each signal transduction pathway that activates c-fos transcription via the SRE acts through a distinct protein complex, with one shared component, the transcription factor SRF, and one or more unique accessory proteins. We have three specific aims. First, using mutagenesis of the c-fos promoter coupled with gene transfer assays, we wish to identify new sequence elements in the c-fos promoter that cooperate with the SRE by providing binding sites for putative accessory factors. Second, using biochemical and molecular approaches, we wish to characterize a series of proteins that we believe may function as accessory proteins for SRF. Third, we wish to begin a detailed biochemical analysis of the organization of the protein complexes that form among these proteins and of the function of these complexes in vivo. We believe that this data will contribute to our understanding of how proliferative signals are processed and how the cell distinguishes among signals with different biological activities. Understanding these control mechanisms will aid in the design of novel therapeutic strategies to deal with proliferative disorders.